Bottom profile

ABSTRACT

This disclosure relates to the bottom profile on a one gallon metal paint can and more particularly to the specific concentric circular re-enforcing bends and beads applied to profile the bottom. In order to increase the static and dynamic strength of the bottom, the selection and position of re-enforcement is essential to maximize resistance to dynamic loadings and static load.

BACKGROUND OF THE DISCLOSURE

This invention is concerned with the design and manufacture of paint canbottoms. Paint cans are over 61/2" in diameter for the popular onegallon size and the can body is made from a flat blank of sheet metalrolled into a cylinder and joined along the meeting longitudinal edge.This rolled cylindrical body is conventional throughout the industry andis manufactured from tinplate. To the body is doubleseamed a circularbottom closure and a top ring designed to receive the top closure orplug.

The present disclosure is concerned with the design and manufacture of abottom end closure which has greater resistance to creasing andfracturing from fatique stress. The standard size 610×703 heightdiameter one gallon paint can is filled with 10 to 13 pounds of paintand tends to be abused in normal packing and shipping. The can makersconvention gives the diameter across the completed doubleseam in inchesplus sixteenths of an inch then the height in inches plus sixteenths ofan inch. Therefore, the foregoing container is 6 10/16" in diameter by 78/16" in height.

More particularly, if a paint container is dropped and/or bumped, it isexpected that the bottom end closure will suffer the greatestdeformation. The bottom end closure buckles or creases radially acrossthe transition between the various areas of the profile. Thesetransitions are usually circular and concentrically located and consistof little more than a series of radii representing and definingre-enforced areas which act to prevent the bottom from flexing orwarping. It should be appreciated that paint cans suffer greaterstresses than other cans of similar design because of their larger sizeand the heavier weight of the contents in them. One easy solution toovercoming dynamic and static loadings is to increase the thickness ofmaterial from which the container bottom end closure is made. That is anunacceptable approach in that more material, more energy and more costfor manufacture and shipping are incurred with that solution. Anotherapproach which has some potential for minimizing the thickness of thecontainer bottom end closure would be to use higher strength materialsand maintain the lighter gauge. This solution is normally unacceptablein and of itself because higher strength materials tend to have lessfatique resistance because of their minimal ductility.

It has been found that the balance between maximum static strength anddynamic strength resides in the overall configuration of profile appliedto the bottom. This configuration or profile is critical to achieving anoverall efficient combination of plate weight, plate type and dynamicand static strength.

OBJECTS OF THE DISCLOSURE

It is an object of the present disclosure to define a bottomre-enforcing profile for a paint can for maximizing the strength andminimizing the material requirements.

It is yet another object of the present disclosure to teach a means bywhich the dynamic or fatique strength of the paint can bottom closurecan be maximized.

It is still a further object of the present disclosure to suggest ameans for producing a low cost, reliable and materially efficient onegallon paint can bottom.

SUMMARY OF THE DISCLOSURE

In accordance with the foregoing objects and in an effort to produce asuperior one gallon paint can bottom closure, a research effort wasundertaken to produce a closure which was tested mathematically andmechanically. Both tests proved that the can bottom of the presentdisclosure is superior in dynamic and static strength parameters eventhough it is constructed of light gauge, higher strength (i.e. harder)metal. In the past, can bottoms have been manufactured from 85 to 100#base box, base weight. The base box terminology for base weight isstandard in the can making industry; it originally referred to theamount of steel in a base box of tinplate consisting of 112 sheets ofsteel 14" by 20", or 31,360 square inches plate. Today the base box asrelated to base weight refers to the amount of steel in 31,360 squareinches of steel, whether in the form of coil or cut sheets. These bottomend closures had a variety of profile configurations none of which wereidentical to that of the present disclosure. In addition to theforegoing, the prior container bottoms had varied performance duringtesting under a flexing load. The dynamic fatique resistance of thebottom closure of the present disclosure was found to be 3 to 4 timesbetter in terms of test-life than the next best competitive design ofany plate weight when this particular test was run. More specifically, atest on a fixture which flexes the bottom more severely than any paintcan would flex in service could not be made to fail. That container wasmade from 85#. DR9 is a tin mill product specification that relates tothe process by which the metal is cold reduced (i.e., DR -DoubleReduced) in two stages with an anneal preformed between the two coldrolling operations. The steel is reduced approximately 89% in the firstreduction, is annealed, and then is reduced about 25 to 40% in thesecond and final cold reduction.

With the preferred profile and 85# DR9 tinplate, the overall bucklestrength is also superior in that such a container end will resist aninternal load of 10-111/2 psi before radial creases appear which aredesignated as a buckle. Although such buckle strength is comparable topresently available plate weights and materials and has been found to beadequate for the performance requirements of a one gallon paint can, theimprovement sought and developed was to maintain buckle strength andincrease fatique strength.

More particularly, the normal criteria for a paint can bottom end designhad been buckle strength. That consideration presumes the strength ofthe end to be sufficient as long as the end does not suffer an abuseduring the handling or shipping. Abuse being defined as a blow whichwould be abnormal and deform the container due to its impact having beensignificantly greater than normal. That sole criteria for bucklestrength does not completely consider the true loadings applied to alarger diameter can end. That is to say that, the cyclic loading whichleads to fatique failure is not normally considered. Fatique failure ofa paint can bottom results from vibrational loadings e.g., transit, bytruck or train shipment or from some paint can mixing shakers. Ofcourse, once the bottom end has been slightly damaged fatique failure ismore likely to occur along a crease or buckle line established by thedamage.

By means of finite element computer analysis (which divides thecross-sectional structure of the bottom closure into a series of piecesadjacent to one another and considers the relative stiffness of eachpiece with respect to its adjacent piece by means of mathematicalcomputer analysis), the stress in any given piece or location of thestructure can be determined. Such an approach was used to isolate theareas of severe or critical stress in existing designs. Once the problemareas were located appropriate corrections had to be found andincorporated in a new design. The new design was then tested by finiteelement computer analysis to determine if the suggested corrections werebest. The ultimate corrections as applied are the subject of the presentdisclosure. More specifically, the free span (unformed center section)of the paint can bottom was reduced. The transition section between thecenter free span and the next adjacent re-enforcing section was softenedby means of a milder slope. The next adjacent section (radially outwardof the transition section) is composed of two portions; the first isflat or normal to the axis of the can body and about one-third of thetotal area and the second is sloped toward the base of the countersinkbead and is about two-thirds of the total area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional view of the bottom profile for a paintcan of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Bottom closures such as the present invention, have introduced intotheir design (profile) panels and radii, for the purpose of addingrigidity and strength. These abrupt variations cause stressconcentrations, a condition where within a very short distance theintensity of stress increases greatly. The 610 bottom closure is madefrom a ductile metal. In ductile metals, a marked plastic deformationcommences at a fairly definite stress (yield point, yield strength,possibly elastic limit). A ductile metal is usually considered to havefailed when it has suffered elastic failure, i.e., when marked plasticdeformation has begin.

Practically all materials will break under numerous repetitions of astress less than that required to produce immediate rupture. Thisphenomenon is known as fatique, which causes a crack to develop andspread, first gradually, then rapidly, until fracture occurs.

The present invention is designed such that the stress levels,especially in areas of stress concentration, have been minimized. Thisaids in minimizing, or eliminating the occurrence of creases (buckles)in abusive handling, and the incidence of fracturing from fatiqueloading, to which all paint cans are subjected.

Turning now to the drawing in FIG. 1, and, in particular, thecross-sectional showing of a paint can bottom profile as same wouldappear before it is seamed on to the rolled body of a paint container.It will be noted that the bottom 10 is positioned as it would be withrespect to a can. That is to say that, it faces upwardly in the area ofthe cover hook 11, as such would be the disposition of it before itmeets the paint container body flange (not shown) for double seaming.The bottom 10 is circular in shape and has a series of concentricallydisposed (about an axis or center line A, shown in phantom) sectionswhich define its overall profile. Each of the respective concentricallydisposed sections is such that the complete bottom represents a seriesof rings or annular portions about the circular center panel of thecontainer. Working inwardly from the cover hook 11 there is a flat rangearea 12 which extends radially inward to an upturned countersink walland adjacent groove 13. These features of the bottom 10 are identical tothose of the prior art and those of earlier containers. The nextadjacent area inwardly of the countersink groove 13 is a flat sectionextending to an inwardly disposed bead both labelled generally 14. Theinwardly disposed bead 14 countersink and cover hook 13 areas representabout 16% of the total area of the container bottom 10. Inwardlyradially and adjacent to the foregoing 16% area is a small transitionsection which angles downwardly very slightly having little or noapparent angularity with respect to a plane normal to the axis A and inthe sense that the bottom 10 would be applied to the container. Thetransition section 15 is about 5 to 6% of the overall bottom area. Itcooperates with the next adjacent section called an outer sloped section16. The outer sloped section 16 continues in the same direction astransition section 15 but at a greater angle. Outer sloped section 16acts much like a leaf spring when the bottom 10 is flexing under adynamic fatique loading.

The combination of section 16 and transition 15 co-act to provideflexibility and stiffness respectively. That is to say that, section 16takes the majority of the flexing and the small stiffer transitionsection 15 acts to provide a more rigid or flex resistant portionbetween section 16 and the outer bead 14. The reason this is so isbecause the outer sloped section 16 has an area of about 30 to 40% ofthe overall area of the bottom. In the preferred embodiment the area isabout 35%. That large free span of gently sloped material has been foundto provide the requisite flexibility to enhance fatique resistance. Thesloped area is angled outwardly relative to the inside of the paint canwhen viewed from the perspective of being higher at its connection pointwith the transition 15 and lower at its radially inwardly most portion.

The radially inwardly most portion of the outer sloped section 16 isconnected to a flat washer-like section 17 having a percentage areaabout one-half of the area of the outer sloped section 16. Flat section17 is provided to act as an inner connecting means between the outersloped section 16 and an inner sloped section 18. More specifically,where outer sloped section 16 angles outwardly with respect to the axisA of the paint can the inner sloped section 18 angles inwardly from itsradial outwardly portion to its radially inward portion with respect tothe container axis A. This inner sloped section 18 is about the samerelative inclination with respect to flat section 17 as that of theouter sloped section 16. Those angles are in the range of about 5° to15° depending on the overall diameter of the container. In the preferredembodiment that angle is 7°-10°. The overall area percentage-wise of theinner sloped section 18 is about one-fourth of that of the outer slopedsection 16 and so the inward axial depth (height up into the can) of theinward radial portion of section 18 is less than the inward axial depth(height up into the can) of the outward radial portion of section 16.

Connected to the inner sloped section 18 and being next adjacent theretoand radially thereof is a circular center panel 19 which is flat and ina plane perpendicular relative to the axis A of the paint can. Thiscenter panel 19 has an area about equal to that of flat section 17.Center panel 19 completes the profile of paint container bottom 10. Tothe extent that center panel 19 is flat and in a plane normal to theaxis A, it is planar. During flexure of the bottom 10 the center panel19 moves in planes normal to the axis A as the flexing is primarily inthe outer sloped section 16.

    ______________________________________                                        PREFERRED EMBODIMENT DIMENSIONS                                               FOR A 610 DIAMETER PAINT CAN BOTTOM PROFILE                                                   OUTER    % OF                                                                 DIAMETER TOTAL AREA                                           ______________________________________                                        CENTER PANEL      2.60"      16.28%                                           INNER SLOPED SECTION                                                                            3.17"       7.86%                                           FLAT SECTION      4.23"      18.88%                                           OUTER SLOPED SECTION                                                                            5.71"      35.35%                                           TRANSITION SECTION                                                                              5.91"       5.56%                                           BEAD AND COUNTERSINK                                                                            6.45"      16.07%                                           ______________________________________                                    

It will be noted that the cover hook and flat flange adjacent theretoare not figured in the above calculations because after double seamingonto a paint can body that area is moved radically inward. Similarly,the angle between the inner sloped section or the outer sloped sectionand the plane of the flat section is about 8° to 10°.

In general, the overall flexibility and resistance to fatique stress ofbottom 10 has been enhanced by a combination of the size and position ofthe various sections of the container bottom. It has been foundnecessary to have the outer sloped section 16 disposed such that it canpermit the necessary flexing and to have it large enough to bedynamically worked without fatique. It is also important that this largeouter sloped section 16 be located radially outward of the center panel19. Flexing of only a large center panel is unsuitable in that itstresses the smaller radially outwardly adjacent areas. Similarly, it iscritical that the sections that connect with outer sloped section 16 bedesigned to cooperate with the overall idea of section 16 beingprimarily the flexible area. Thus, the transition 15 and the flatsection 17 are included and kept with minimal angularity relative tosection 16 to provide somewhat greater stiffness without a concentrationof stress at their respective junctures.

It is, therefore, the purpose of the claims which follow to cover anycontainer bottom which has the overall general configurational shapeand, more specifically, concentric sections designed to flex and thuscarry dynamic loadings applied to such container bottoms. Morespecifically, the countersink and cover hook areas have to be rigid asdoes the outer bead area relative to the overall flexibility of thebottom 10. The center panel 19 must operate in such a fashion that itcan move axially inwardly and outwardly without significant change incross-sectional configuration flexure. It is necessary that the annularor ring sections between the center panel 19 and the outer radial mostsections or rim of the bottom will act as spring members to permit theoverall flexing of the bottom. The spring portions of these sectionshave to be tempered with connecting junctures that tend to damp thespringing near the connections to the more relatively rigid portions ofthe bottom. Therefore, the claims which follow seek to cover theaforesaid concepts in their broadest context without regard to thespecific material or the actual dimensions necessary for a particularembodiment.

What is claimed is:
 1. A bottom end closure for a thin wall hollowtubular cylindrical container body such as for containing paint whereinsaid end closure being formed from a thin disc of metal and adapted tobe double seamed to said body and having a series of sectionsconcentrically positioned relative to the center of said disc formedinto said closure, disposed radially relative to each other andextending from a planar center panel to a countersink groove associatedwith a cover hook being that portion of said end for double seaming tothe body when the axis of same is aligned with said center and whereinthe profile defined by said sections being the improvement to enhanceresistance to dynamic loadings caused by flexure of said end closurecomprising:a countersink groove positioned radially inwardly of thecover hook for double seaming, a bead facing and opening outward of saidbody and positioned inwardly of said countersink groove for acting toresist flexure by increasing stiffness of the area thereabout; atransition section located radially inwardly of said bead and beingconnected thereto and having a sloped inclination outwardly of said bodyand with an area of 5 to 6 percent of said double seamed end; an outersloped section of said end located radially inwardly of said transitionsection sloped with a uniform frusto conical surface configurationextending toward the axis of said body yet angled outwardly of theinterior thereof and more so than said transition section and having anarea of about 30 to 40 percent thereof when double seamed, a flatwasher-like section located radially inwardly of said outer slopedsection and carried in a plane normal to the body axis with anangularity relative to said outer sloped section in the range of about5° to 15° and having an area of about one-half the area thereof whereinthe portions of said end which thus bound said outer sloped section havegreater stiffness and are connected thereto with minimal angularityencouraging flexure across said outer sloped section, and; a centerpanel of said end connected to said flat washer-like section formovement of said center panel through planes perpendicular to the axisof said body thereby controlling the dynamic response of said endclosure.
 2. The end closure of claim 1 wherein the boundary of theinnermost radial portion of said outer sloped section is circular andconnects to said flat washer-like section which lies in a planesubstantially normal to said axis of said body and the boundary of theinnermost radial portion of said washer-like section is circular andconnects to an inner sloped section being an upward inwardly frustoconically shaped surface which extends to the outer radial circumferenceof said circular center panel.
 3. The end closure of claim 2 whereinsaid frusto conically disposed sections intersect with said ring shapedsection at angles of 7° to 10° relative to said plane thereof.
 4. Theend closure of claim to 3 wherein said circular center panel is planarand about one-half the total area of said outer sloped section.
 5. Theend closure of claim 4 wherein said washer-like section is about equalthe area of said center panel.
 6. The end closure of claim 5 whereinsaid inner sloped section is about one-half the area of said centerpanel.
 7. The end closure of claim 6 wherein said transition section isabout one-third the total area of said center panel.